In a rotary-type valve such as a ball valve, plug valve, butterfly valve, etc. a stem is rotated for operating the closure member between open and closed positions. It is known in such valves to employ a frangible element such as a shear pin adapted to fail and prevent excessive torque from being transmitted to the valve mechanism. Exemplifying the use of shear pins in a rotary valve are the disclosures of U.S. Pat. Nos. 3,701,362; 4,072,161; and 4,141,538.
Characteristically, when failure of the shear pin occurs in such prior art constructions, it is necessary to drive out the separated pin pieces and insert a new pin to restore the valve to its operational condition. Even where the underlying cause of overtorque may dissipate without servicing the valve or where the cause stems from a weakness in the pin itself, this prior art procedure requires on-hands access to the valve per se for driving out the pin pieces. Many times, however, there are instances in which such valves are installed underground in a pit, valve box or the like, for which on-hands access to restore the frangible pin is most difficult and some times virtually impossible without extensive excavation or whatever. Needless to say, delayed inability to operate the valve under those circumstances, particularly when the valve is used to control utility services such as gas or water, represents not only an inconvenience and/or major expense, but a potential hazard as well.
Despite recognition of the foregoing, it has not heretofore been known how to overcome the frangible element replacement problem for valves utilized in underground service.